Why not vertical?

[JAZZCNC]

The only problem I can think of, is holding parts that are cut clean out. no tabs etc. at best, the parts will fall on the floor, at worst, they will trap the cutter and maybe snap it.

Not a problem at all. It's actually better than when horizontal. When horizontal the cutter will try to fling the part just the same with exactly the same consequences if tool gets trapped. Even when horizontal the required parts need to be held securely other wise it's a lottery if they will be damaged or not. Waste parts can be left lose but it's a lottery to what happens with them, they too can trap tools.
Being vertical the lose part drops away far easier than when in horizontal position and if for any reason it does clash with tool it gets flicked away far easier.
Also because most of the chips etc are falling away then there's virtually no chips clogging the slot again leaving the part to be ejected easier.

Put it this way it's not snapped any yet or even remotely looked like doing and it's cut plenty of Aluminium, Brass, copper, wood, plastic since being on the wall.
The cutters are lasting longer, the finish is better due to virtually no chip re-cutting and I need much less blown air to clear the remaining chips and best of all 90% the chips fall neatly into a bin on the floor.

[TrickyCNC]

Not a problem at all. It's actually better than when horizontal. When horizontal the cutter will try to fling the part just the same with exactly the same consequences if tool gets trapped. Even when horizontal the required parts need to be held securely other wise it's a lottery if they will be damaged or not. Waste parts can be left lose but it's a lottery to what happens with them, they too can trap tools.
Being vertical the lose part drops away far easier than when in horizontal position and if for any reason it does clash with tool it gets flicked away far easier.
Also because most of the chips etc are falling away then there's virtually no chips clogging the slot again leaving the part to be ejected easier.

Put it this way it's not snapped any yet or even remotely looked like doing and it's cut plenty of Aluminium, Brass, copper, wood, plastic since being on the wall.
The cutters are lasting longer, the finish is better due to virtually no chip re-cutting and I need much less blown air to clear the remaining chips and best of all 90% the chips fall neatly into a bin on the floor.

Interesting to here what actually happens in practice.
I only cut wood, so the edges might get dinged falling on the floor. Although I tend to used the 'onion skin' method, and break out the parts after cutting.

I did think about it before I posted, and thought the cutter would be fine most of the time, but the the cut finished under the part, then the part would fall on the cutter bit.

Luckily I've not had any trouble with broken bits yet (I know I shouldn't say that) but I have seen the warnings from the bit suppliers about parts moving when cut free.

[JAZZCNC]

I only cut wood, so the edges might get dinged falling on the floor. Although I tend to used the 'onion skin' method, and break out the parts after cutting.

I did think about it before I posted, and thought the cutter would be fine most of the time, but the the cut finished under the part, then the part would fall on the cutter bit.

But the trick (no pun) is not to let the wanted part fall lose and like I said that holds true for when horizontal. Yes you can and I have many times held parts by hand when coming to the end of cut so it doesn't get pulled back into the cutter or fall on it but that's just the same when vertical and with either your playing a lottery to the part getting damaged if you don't. When normal cutting then it's not a problem because all is held secure.
The onion skin approach is one I use also in some circumstances but others it's not an option so then other tactics are needed, like double sided tape. (I actually cut a 14x19" 3mm and £100 quids worth of brass plate just held with tape in the vertical . . Scary ASF but worked a treat.!!)
Tabs are good has well along with strategicly placed holes for screws.!!

The falling onto the tool never happens because I control the lead in lead out point and make sure it's on the side or top.!